Stabilization of chlorinated hydrocarbons



'been practiced for many years.

United States Patent STABILIZATION OF CHLORINATED HYDROCARBONS Fred W. Starks, Tonawanda, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware N0 Drawing. Application July 23, 1954,

Serial No. 445,461

V 12 Claims. (Cl. 260-6525) This invention relates to chlorinated hydrocarbons stabilized by the addition thereto of small amounts of certain chemicals.

The removal of grease films from metallic surfaces has Generally the removal is accomplished by suspending the metal to be degreased in a boiling fat-solvent at atmospheric pressure. Suitable fat-solvents including particularly the chlorinated hydrocarbons, of which trichlorethylene, perchlorethylene, tetrachlorethane and ethylene chloride are representative, but others may be utilized as well.

Trichlorethylene is probably the solvent most widely used in such operations. It is, however, seldom used in the pure state. Instead, stabilizing agents are usually added to prevent decomposition under the conditions of storage and utility. Light and oxygen, for example, decompose trichlorethylene very rapidly. Heat is also deleterious to this solvent and may accelerate the effects of light and oxygen. Unless precautions are taken, decomposition from heat, light and oxygen takes place under ordinary conditions. This type of decomposition may,

therefore, be called normal. Many compounds are known which, in trace amounts, will inhibit normal decomposition. 1

Another type of decomposition occurs when the workpiece to be degreased is made of aluminum or an aluminum alloy. The stabilizers effective to prevent decomposition by oxygen, light or heat are, in general, powerless against decomposition caused by aluminum. Resultant solvent degradation is evidenced by a rapid rise in acidity and by pronounced discoloration. In advanced stages, there is formed a black, tarry mass which may deposit on the workpiece. The same phenomenon can be observed in iron degreasing but to a much lesser extent.

The causes of this metal-induced decomposition are not definitely known. One explanation is that an accumulation of non-volatile oils removed from the workpiece during the degreasing process may raise the boiling point of the liquid. The increase in temperature may then result in a reaction between the finely divided metal washed off the surface of the workpiece and trichlorethylene. An alternative explanation is that the large surface presented by the finely divided metal catalyzes the decomposition. There is also the possibility that a metal chloride such as aluminum chloride or ferric chloride may be formed and act as a decomposition agent. In any event, it has heretofore been necessary to shut down operations and to remove the non-volatile oil and metal fines at frequent intervals. Such shut-downs entail additional labor, loss of production, and loss of solvent and hence detract from the economics of the degreasing process.

A major object of this invention is, therefore, provision of a novel and useful method of stabilizing chlorinated hydrocarbons.

Another object is provision of a method for stabilizing 2.0 g. of aluminum metal chips.

ice

2 chlorinated hydrocarbons against decomposition induced by metals, aluminum in particular.

An additional object is provision of a chlorinated hydrocarbon stabilized against decomposition induced by aluminum. 7

The above mentioned .and still further objects may be accomplished in the spirit of this invention by' adding to the chlorinated hydrocarbon designed as adegreasing solvent a small amount of a cyclic sulfone.

The cyclic sulfones of this invention are compound possessing the configuration: i

where R represents a saturated orunsaturated divalent organic aliphatic hydrocarbon radical, preferably of the alkylene type. Of particular value is butadiene cyclic Other cyclic sulfones of the alkylene typeare pentadiene and hexadiene cyclic sulfones. No acyclic sulfone tested was effective in preventing the aluminum-catalyzed decomposition.

The quantity of sulfone required for elfective stabilization of the chlorinated hydrocarbons is not very great but will vary to some extent with the individual compound chosen In general between about 0.5% and 5% by weight of the additive is eifective. The sulfones are compatible with stabilizing agents normally used .in chlorinated hydrocarbons. Consequently, mixtures of these agents with sulfones may readily be employed.

There follow some examples which illustrate details of the invention. In these examples the presence of aluminum metal and aluminum chloride simulates operating conditions in a metal degreaser. All pressures are those of the ambient atmosphere unless otherwise noted.

Example 1 This example shows the decomposition of trichlorethylone containing no sulfone during aluminum degreasing operations and is included as a control.

(a) Fifty milliliters of freshly distilled trichlorethylene was heated to the reflux temperature of the solvent in the presence of 0.5 g. anhydrous aluminum chloride and After a reflux of one minute the solvent had turned black and a tarry substance had been deposited on the walls of the container.

(b) The experiment of 1(a) was repeated except that the trichlorethylene utilized contained a small percentage of N-methyl pyrrole. This compound is a widely used antioxidant effective against normal air, light and heat decomposition. In the present test, the clear liquid blackened and deposited a black insoluble material in a reflux period of 1-2 minutes.

Example 2 This example shows the efiectof the preferred additive of this invention, butadiene cyclic sulfone.

Fifty milliliters of freshly distilled trichlorethylene containing 1.8 g. of butadiene cyclic sulfone was refluxed for 3.5 hours in the presence of 0.5 g. of aluminum chloride and 2 g. of aluminum chips. Neither discoloration nor deposition of tar occurred.

Having described my invention, I claim:

1. The method of stabilizing a chlorinated hydrocarbon of the group consisting of trichlorethylene, perchlorethylene and tetrachloi'ethane which comprises supplying thereto an amount effective to stabilize the same against decomposition induced by metals and metallic salts of a cyclic sulfone of the formula where R is a divalent aliphatic hydrocarbon radical possessing a carbon chain 4-6 carbon atoms in length.

2. The invention of claim 1 in which the sulfone comprises about 0.5'5% by Weight of the chlorinated hydrocarbon and possesses an aliphatic chain four carbon atoms long.

3. The invention of claim 2 in which the cyclic sulfone is butadiene cyclic sulfone.

4. The method of stabilizing trichlorethylene which comprises supplying thereto about (LS-5% by weight of butadiene cyclic sulfone.

5. The method of stabilizing erchlorethylene which comprises supplying thereto about 0.5-5 by Weight of butadiene cyclic sulfone.

6. The method of stabilizing tetrachlorethane which comprises supplying thereto about 0.5-5 by weight of butadiene cyclic sulfone.

7. A chlorinated hydrocarbon of the group consisting of trichlorethylene, perchlorethylene and tetrachlorethanc containing an amount eifective to stabilize the same 4 against decomposition induced by metals and metallic salts of a cyclic sulfone of the formula where R is a divalent aliphatic hydrocarbon radical possessing a carbon chain 4-6 carbon atoms in length.

8. The invention of claim 7 in which the cyclic sulfone comprises about 0.55% by weight of the chlorinated hydrocarbon and possesses an aliphatic chain four carbon atoms long.

9. The invention of claim 8 in which the cyclic sulfone is butadiene cyclic sul'fon'e.

10. Trichlorethylene containing about 0.55% by weight of butadiene cyclic sulfone and thereby stabilized against metal-induced decomposition.

l1. Perchlorethylene containing about 0.5-5 by weight of butadiene cyclic sulfone and thereby stabilized against metal-induced decomposition.

l2. Tetrachlorethane containing about 0.5-5 by weight of butadiene cyclic sulfone and thereby stabilized against metal-induced decomposition.

References Cited in the file of this patent UNITED STATES PATENTS 2,371,645 .Aitchison et al. Mar. 20, 1945 

1. THE METHOD OF STABILIZING A CHLORINATED HYDROCARBON OF THE GROUP CONSISTING OF TRICHLORETHYLENE, PERCHLOETHYLENE AND TETRACHLORETHANE WHICH COMPRISES SUPPLYING THERETO AN AMOUNT EFFECTIVE TO STABILIZE THE SAME AGAINST DECOMPOSITION INDUCED BY METALS AND METALLIC SALTS OF A CYCLIC SULFONE OF THE FORMULA 